DETECTION OF LATENT INFECTIONS OF RALSTONIA SOLANACEARUM BIOVAR 2, RACE 3 IN TOMATO CROPS

A protocol was set up to detect latent infections of Ralstonia solanacearum biovar 2, race 3 in field tomatoes. For two growing seasons, healthy tomato plants were inoculated with a virulent strain, and monitored for between 7 and 55 days. Final extracts used for direct isolation on Kelman's medium and for indirect immunofluorescence staining, were prepared from 1 cm segments collected from the base of the lowest side shoots. Reisolations were identified by colony morphology, PCR, IFAS, and pathogenicity tests on tomato plantlets. Reisolation was successful from 18 days onwards, with a frequency that constantly increased in the following weeks. Samples prepared by mixing one latently infected segment with increasing numbers of healthy segments revealed a sensitivity threshold of 1: 999. This non-destructive protocol was shown to be appropriate for monitoring in the open field.